With the advance of technology relating to medical diagnosis and therapy, there is an on-going need to improve methods and systems for sensing chemical parameters, particularly in a medical context both outside and within the body. There is also a need more generally to improve the sensitivity and cost effectiveness with which various chemical species can be detected.
There are many optical techniques known in the art for sensing various chemical parameters. For example, U.S. Pat. No. 5,132,057 discloses an optical fiber probe based on the immobilisation of fluorescent dye in a hydrogel at the distal end of the optical fiber. The dye is excited by passing light to it from the optical fiber and the intensity of the fluorescence is monitored to give an indication of blood pH.
It is also known from U.S. Pat. No. 5,804,453 to immobilise a reagent such as an antigen layer at the end of an optical fiber. When placed in a solution containing the complementary antibodies, an antibody layer binds to the antigen layer. This growth in the immobilised layers is detected by a change in the phase difference between light reflected from the fiber/reagent boundary and the distal edge of the immobilised layers respectively.
Furthermore U.S. Pat. No. 5,898,004 discloses a device composed of a crystalline colloidal array polymerized in a hydrogel. Swelling of the hydrogel in response to stimuli is measured as a shift in the Bragg diffraction wavelength.
There remains a need, however, for a highly sensitive probe capable of sensing a wide range of chemicals. Accordingly, when viewed from a first aspect the present invention provides an interferometric chemical sensing probe comprising or for mounting to an optical fiber, and a chemically responsive measuring material adapted to exhibit a change in volume and/or refractive index in the presence of a given chemical so as to produce a change in at least one optical path length through the probe.